How Does an Electric Generator Work?

Faraday's Law

• Electric generators work because of the effects described by Faraday's Law. This Law is used in the design of numerous electric devices, but for generators it is important because it describes the effects of moving a magnet inside a coil of conductive wire.

Generating Electricty

• The typical generator design uses either one or a set of electromagnets on a shaft. Therefore it requires an outside source of electricity to get started. These are placed inside a coil of conductive wires that are arranged to form a cylinder. The shaft rotates, turning the magnets and their electromagnetic fields. In accordance with Faraday's Law, the changing movement of the electromagnetic field through the conductive materials causes each part of the wire to build a charge. Combined, these can become quite a substantial charge. This electric charge is then transmitted out of the generator.

  Converting Mechanical Power to Electricity

  • Generators use the process described above to convert mechanical energy into electricity. The mechanical energy is what turns the shaft upon which the electromagnets are mounted, and there are a variety of sources used to provide this mechanical, turning motion. Most power plants are thermal power plants. These use a source of heat, such as burning fossil fuels or a nuclear reaction, to boil water into steam. The hot jet of steam passes through a turbine, turning its blades and providing a source of mechanical power, which is then transferred to the generator to turn the shaft. Wind turbines capture the kinetic energy of the wind to turn the shaft, whereas hydroelectric plants do the same thing with the energy of moving water. A portable generator does not burn gasoline to boil water in the same way that a thermal power plant does, but instead uses the mechanical power of an internal combustion engine to turn the shaft.

  Efficiency

  • The typical power plant has an efficiency of 35 percent. That means the conversion of heat or kinetic energy into first mechanical and then electrical energy produces 35 units of usable power for every 100 units put into the process. That might not sound like a lot, but it is actually very good compared to a variety of other machines. A car engine, for example, only has an efficiency rating of about 20 percent.